To obtain more optical power for industrial applications than can be provided by a single laser bar, arrays of vertically or horizontally stacked laser diode bars are typically required. Because a typical laser bar emits on the order of tens of W of heat in a very small volume, it is conventional practice to mount the laser bar on a heat sink and, more particularly, on a water-cooled microchannel heat sink whose copper channels offer a large surface area for heat transfer to the cooling water. When laser diode bars together with their microchannel heat sinks are vertically stacked for greater optical power, they are usually connected electrically in series. To connect the stack of laser bars in series, adjacent heat sinks are separated by a layer of electrically insulating material whose thickness is approximately the same as that of a laser diode bar. In such arrangements, adjacent components are placed as close together as possible to maximize the optical intensity of the emitted light beams. However, the minimum spacing between adjacent light beams emitted by the stack of laser bars is determined by the thickness of the components and the heat dissipating capacity of the stack. The best available separation between adjacent components in the stack (or array), whether the components are individual laser diodes or laser diode bars, is about 1.2 mm which is capable of producing a power density of 200 watts/sq. cm.
It has heretofore been proposed in U.S. Pat. No. 5,987,043 to increase optical power density by employing a stack of heat sinks having diode bars mounted at the ends of the heat sinks instead of at the top edges of each so that adjacent emitted light beams can be closer than the thickness of the heat sinks. Alternatively, as shown in German patent DE 2,153,969 and Japanese patent JP 4,426,789 each laser bar may be mounted on a respective step of a shared, staircase like, water-cooled heat sink. In the more recently-issued U.S. Pat. No. 6,229,831 a shared heat sink having a triangular cross-section was employed together with a triangular submount for each of the laser diode bars, the angle of the submount complementing the angle of the triangular heat sink.
Unfortunately, mounting a laser bar at the end of a microchannel heat sink, as shown in FIG. 2 of the '043 patent, is not as efficient from the standpoint of maximum heat transfer as mounting the laser bar at the top edge of the heat sink. Furthermore, vertically stacked arrays of serially-connected microchannel heat sinks leads to unexpected corrosion problems in the water path that reduce the effective life of the heat sink. On the other hand, the '831 patent states that because of the difficulty of manufacture, the use of microchannel heat sinks is not possible with a “staircase” configured array of laser bars.